Size collectors, estimate output, and compare savings confidently. Built for accurate planning across homes, hotels, clinics, and facilities.
| Scenario | Water Use (L/day) | Inlet (°C) | Target (°C) | Irradiance (kWh/m²/day) | Efficiency (%) | Losses (%) |
|---|---|---|---|---|---|---|
| Small home | 150 | 22 | 55 | 4.8 | 52 | 15 |
| Family house | 250 | 20 | 60 | 5.4 | 56 | 14 |
| Guest house | 500 | 18 | 60 | 5.8 | 58 | 13 |
| Clinic block | 900 | 19 | 65 | 5.6 | 60 | 12 |
1) Daily hot water energy demand
Qdemand = (L × 4.186 × ΔT) / 3600
Here, L is daily hot water volume in liters, ΔT is the temperature rise in °C, and 4.186 is water specific heat in kJ/kg·°C. The result is daily heating energy in kWh.
2) Useful solar gain per square meter
Qsolar,m² = G × η × (1 − losses) × orientation factor
G is average solar irradiance in kWh/m²/day. Efficiency, losses, and orientation values are converted from percentages into decimals.
3) Required collector area
A = Required solar energy / Useful solar gain per square meter
Required solar energy equals daily demand multiplied by desired solar fraction. This estimates the collector area needed to cover the selected load share.
4) Recommended storage tank size
Tank volume = Collector area × Storage factor
Storage factor is commonly expressed in liters per square meter. It helps match storage capacity with collector output and usage patterns.
Solar fraction is the percentage of your water heating demand covered by solar energy. A 70% solar fraction means solar energy supplies 70% of the annual heating load, while backup heating covers the remaining 30%.
Lower inlet temperature increases the required temperature rise. That raises daily heating energy demand and usually increases the collector area needed to meet the same hot water target.
Flat plate systems often operate around 45% to 65% under practical conditions. Evacuated tube systems can vary differently. Actual performance depends on climate, temperature difference, flow rate, and installation quality.
Losses account for piping heat loss, tank standby loss, controller behavior, and imperfect heat transfer. Ignoring them can oversize expected performance and lead to unrealistic savings estimates.
Orientation factor adjusts performance for collector tilt and azimuth relative to ideal solar exposure. Poor orientation lowers useful solar gain, even if collector area and efficiency remain unchanged.
Storage factor links tank volume to collector area. Higher storage can smooth solar availability, but oversized tanks may increase standby losses. Many domestic systems use moderate liters-per-square-meter values for balance.
Yes. It converts solar thermal output into avoided backup energy use, then multiplies that saved energy by your electricity tariff. The estimate improves when your tariff and heater efficiency inputs are realistic.
It is useful for preliminary sizing and feasibility checks. For commercial design, engineers should also assess hourly demand profiles, seasonal weather data, stagnation control, code requirements, and detailed hydraulic design.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.